The invention relates to rubber compositions comprising a rubber compound and a processing additive, to a method of preparation thereof, and to a method of use of such rubber compositions in mechanical rubber goods, particularly in tyres.
Many various chemicals, usually referred to as “Rubber Chemicals and Additives”, are used in manufacturing of rubber-elastic materials. They serve to simplify and facilitate the compounding process, to control the elastomer properties of the compounded rubber material, and to protect the material during compounding, and thereafter as finished product, from deterioration. Among these are vulcanisation chemicals which support crosslinking of the rubber, particularly sulphur, sulphur donors, and peroxides, activators such as zinc oxide, and accelerators such as sulphenamides, thiazoles, thiurams, and dithiocarbamates. Hardness of the rubber compound can be influenced by fillers, among which carbon black and the so-called white fillers, mainly silica, calcium carbonate, and kaolin are noted.
If carbon black is used to increase the hardness of a rubber composition, the viscosity of the rubber mixture is also largely increased which adversely affects the mixing process. Plasticisers are used in such case to reduce the viscosity, mostly mineral oils, the so-called process oils. However, mineral oils remaining in the ready-made rubber compound reduce the hardness and stiffness. It is therefore an object of the invention to provide a replacement for process oils that is able to reduce the viscosity of the rubber composition during mixing, but does not lead to lower hardness and stiffness of the rubber composition, and of vulcanised parts made therefrom. Particularly, it is desired to provide a replacement for process oils that allow to make mechanical rubber goods with a high stiffness and bending strength. Such strength and stiffness are particularly needed in the apex region of tyres which is a part of the bead area of a tyre which also ensures the seating of the tyre on the rim.